The production of biologically active polypeptides and proteins is important economically for the manufacture of human and animal pharmaceutical formulations, enzymes, and other specialty chemicals. Recombinant DNA techniques using bacterial, fungal, mammalian, or insect cells as expression hosts are particularly useful means for producing large quantities of polypeptides.
Recombinant production of desired proteins generally involves transfecting host cells with an expression vector that contains signals which, when operably linked to a gene encoding the protein, control expression of the gene. The cells are grown under conditions suitable for expression of the recombinant protein. The expression control signals typically include a promoter, which influences the rate at which a gene located downstream of the promoter is transcribed into RNA and determines the transcriptional start site. Expression control signals are chosen so as to be functional in the host cell used for production of the desired protein. For instance, the bacterium E. coli is commonly used to produce recombinant proteins in high yields. Numerous references disclose methods of using E. Coli and other bacteria to produce proteins recombinantly. (see, e.g., U.S. Pat. Nos. 4,565,785; 4,673,641; 4,738,921; 4,795,706; and 4,710,473).
For recombinantly produced proteins that are intended for commercial use, in particular, it is desirable to obtain a high level of expression of the desired protein from the host cells. Increasing the amount of desired protein produced per cell can reduce costs of production due to the decreased volume of cells that must be grown to obtain a given amount of product, and also can facilitate purification because the desired product makes up a larger percentage of the total protein produced by the host cells. Therefore, a need exists for expression control signals that are capable of expressing a desired protein at high levels. The present invention fulfills this and other needs.